The objective of this project is determination of the clinical significance of data derived from a previously developed device (Fratantoni, et al, Quantitative assessment of platelet morphology by light scattering: A potential method for evaluation of platelets for transfusion. J Lab Clin Med 103:620, 1984). The device measures the degree of disc-like morphology of platelets, a parameter believed to correlate with normal platelet function. The measurement is made without violating the integrity of the platelet container. The device will be used to obtain measurements on platelet units intended for transfusion into patients. A sample of the platelet suspension will also be tested in an in vitro device that emulates a bleeding time measurement. This is accomplished by forcing the platelet suspension through an orifice in a membrane that has been coated with collagen and noting the time required for a platelet plug to form. Clinical measurements of hemostasis will also be obtained from the patients for 48 hours following transfusion. The data will be analyzed to determine whether the light scattering device provides any predictive information on the behavior of the platelets. If this is the case, the device may have value in routine blood bank use.